The goals of surgical intervention in children with PHN are relief of obstruction, preservation of renal function, and prevention or alleviation of symptoms. The challenge lies in attempting to determine which PHN patients will go on to require surgery based on the minimal information available at early or baseline visits. Traditionally, the degree of HN noted on the initial US will help determine the need and value of further diagnostic investigations to further elucidate the etiology of the dilatation. This may include a VCUG and nuclear renograms, both of which provide valuable information but are invasive (as they require catheter dopamine beta hydroxylase or intravenous access) and incur radiation exposure. The ability to predict which children are most likely to undergo surgical intervention based on early US imaging may allow for more selective ordering of invasive tests, closer monitoring of those who meet surgical risk factors, and customized parental counseling. This selectivity also provides an opportunity for minimizing radiation exposure and maximizing a value-driven approach to patient care, potentially alleviating institutional financial burdens.
Previous studies evaluating surgery as an outcome in infants with PHN frequently employ renogram results as the main indication for surgery, primarily low baseline DRF, a decrease in DRF on serial renal scans, or a prolonged t1/2 time. Alternatively, attempting to find cutoff values for renal US measurements, namely APd and ureteric diameter, to predict surgical intervention has also been explored. Arora et al reviewed a series of infants with PHN and reported that APd >24 mm was a strong predictor of surgery; however, they cautioned using APd alone as a surgical indication and rightfully suggested closer monitoring of these patients. Similarly, a postnatal APd cutoff of >16 mm was suggested as predictive of the need for pyeloplasty by Dias et al. Both of these studies reported on infants with UPJO-like PHN requiring pyeloplasty. Braga et al reviewed a series of primary nonrefluxing megaureter patients and reported that ureteric dilatation of >17 mm was a strong predictor of surgery in infants with HUN. It should be noted that in each of these studies, most children were monitored over several months and cutoff measurements were based on trends of worsening dilatation. These measurements provide a good guideline, yet the discrimination comes from serial monitoring, and use of dilation measurements fails to take into account an important aspect of US imaging, the renal parenchyma. Therefore, it is noteworthy that the most commonly employed classification schemes (SFU and UTD), although somewhat subjective, take into account and consider the US characteristics of the kidney. The conceptual basis for the present work is to validate an objective measure that captures in a single number the relationship between the degree of dilation and the amount of renal parenchyma.
Our results indicate that measuring PHAR at baseline US allows for early identification of patients who are more likely to undergo surgical intervention, information that is gathered before serial US and renal scan results are available. Furthermore, PHAR values appear to correlate with future nuclear scan parameters, suggesting that there is potential for correlation with renal function and drainage tests. These exciting results are comparable with a recent study by Cerrolaza et al and provide basis for further evaluating the value of more sophisticated, objective US determinations.
The use of US-derived area estimates is not new, and our work is based on previous pioneer studies. For example, estimation of RPA using image software and routine US images has been used to predict those at risk for developing chronic kidney disease in children with PUV as well as to estimate renal loss post-UTI in children with VUR. In fact, using this tool to predict the need for pyeloplasty by measuring the parenchyma to pelvis ratio has been reported previously by Rodríguez et al, in a study published over 15 years ago. After reviewing a series of 81 patients, they found that a parenchyma to pelvic area ratio of 1.6 on baseline US was indicative of the need for pyeloplasty in their limited series of patients. By reviewing a large number of patients prospectively enrolled and including both isolated UPJO-like HN as well as those with HUN, we found PHAR cutoff value of <5.5 to be predictive of the need for surgery. As such, we attempt to rekindle interest in this ultrasonographic parameter and further define PHAR values for detecting surgical patients. These efforts continue to validate the utility of this diagnostic finding.